Integrated circuits (ICs) comprising many tens of thousands of semiconductor devices including field effect transistors (FETs) are a cornerstone of modern microelectronic systems. A common active device within an integrated circuit is the metal-oxide-semiconductor field effect transistor (MOSFET). A MOSFET typically comprises a gate stack composed of a gate electrode and an underlying gate dielectric. The gate stack is formed over a semiconductor substrate with a source and a drain diffusion region formed within the substrate on opposed sides of the gate stack. A channel region is located under the gate dielectric and between the source and drain regions. During operation, the channel region is converted to an “inversion mode” where a conductive path is formed to link the source and drain when a voltage is applied to the gate electrode.
One of the factors influencing the amount of current flow through a MOSFET channel is the mobility of carriers within the channel region. Specifically, an increase in the mobility of carriers in the transistor channel leads to a higher current during operation and a correspondingly faster device operation. Therefore, semiconductor device structures and methods of fabrication that lead to increased mobility of carriers in the channel region are desirable.